The invention relates to a gas bag module for vehicle occupant restraint systems.
Known gas bag modules communicate with a gas generator which upon its activation provides a pressurized hot gas passed into the gas bag to inflate the same. Because of the elevated temperature the hot gases can damage the material of the gas bag wall so that the gas permeability of the gas bag is changed in an unwanted manner and its restraint function can be impaired. Burn injuries of the vehicle occupant can also occur because of the uncontrolled release of the hot gases.
In order not to damage the gas bag fabric when the propellant charge is ignited, there are various conceptions effecting that the hot gas cannot damage the gas bag wall. According to one conception, a heat-degrading agent is used which is provided on the inner surface of the wall of the gas bag. Upon contact with the hot gases the heat-degrading agent is subjected to a physical or chemical change of its state of matter or its structure, thermal energy being taken up. As a result; the temperature of the gases is lowered before the gases come into contact with the fabric from which the gas bag wall is made. The heat-degrading agent can be plastic threads which are interlaced in the gas bag fabric. The threads can either be made of a material having a melting point lower than that of the gas bag material or the threads may be made from a material the same as that of the gas bag but only with roughened and thus enlarged surface. Because of the lower melting temperature or the greater contact surface the interwoven threads in front of the gas bag wall start melting. In another conception, the inner wall of the gas bag is dusted with a substance which decomposes from a certain temperature on and which takes the thermal energy necessary for the decomposition reaction from the gas. In another conception, a separate fabric layer is inserted in the interior of the gas bag, which layer prevents a direct contact of the hot gas with the wall of the gas bag.
In order to obtain a flame protection for the wall of the gas bag, a material differing from the actual wall material is inserted in the gas bag in all of these conceptions. This requires markedly increased production costs.
The object of the invention consists in further developing a gas bag of the initially mentioned kind so as to obtain a flame protection with less expenses and less costs.
This is achieved in a gas bag module which comprises at least a first fabric layer which is made of interwoven weft threads and warp threads and which forms a wall of a gas bag. The gas bag module further comprises a gas lance which is provided with openings for an inflow of a gas into the gas bag and at least a second fabric layer. The second fabric layer is disposed in the area of the openings and is formed by part of the weft threads of the first fabric layer. The conception underlying the invention consists in xe2x80x9cbranching offxe2x80x9d part of the weft threads of the gas bag wall to obtain a flame-protecting fabric layer. Thus, the flowing-in hot gas first strikes upon the second fabric layer in the area of the openings and protects the actual gas bag wall from the flowing-out hot gas. The additional fabric layer can be destroyed by the elevated gas temperature without the restraint function of the gas bag being impaired by this. Since the second fabric layer serving as a flame protection is no separate part but can be produced in the same phase of operation when the wall of the gas bag is woven, the production costs are especially low.